Preparation,homogenization, and storage of earth standards used and distributed by the International Humic Substances Society     

Wesley L. Campbell  Mollie J. Malcolm 《Organic Geochemistry》1985,8(1):109

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Petrogenesis of Archean lamprophyres in the southern Vermilion Granitic Complex,northeastern Minnesota,with implications for the nature of their mantle source   总被引：1，自引：0，他引：1  

G. Wesley McCall  Peter I. Nabelek  Robert L. Bauer  Michael D. Glascock 《Contributions to Mineralogy and Petrology》1990,104(4):439-452

Petrogenetic modeling of major and trace element and isotopic data is used: 1. to define probable modes of petrogenesis of Archean spessartitic lamprophyric rocks in the southern portion of the Vermilion Granitic Complex (VGC) of northeastern Minnesota, and 2. to place constraints on the nature of the mantle source of these rocks. The lamprophyres range from olto qtz-normative and are associated with cumulate hornblendites and pyroxenites. The silica-rich lamprophyres are shown to be the result of low-pressure fractionation upon emplacement. On the other hand, the composition range of the ol-normative lamprophyres is explained by approximately 40% polybaric fractionation of elinopyroxene + olivine yielding ne-normative liquids. The fractionation explains low Cr, Ni and Sc concentrations compared to primary mantle-derived melts. Modeling of the lamprophyre MgO?FeO compositions using the olivine saturation surface (Hanson and Langmuir 1978) suggests that the 0.42 to 0.55 Mg/(Mg+Fe) ratios of most of the lamprophyres can be explained by the high-pressure fractionation. The model parent melt composition is similar to sanukitoid-type rocks found in Japan and elsewhere in the Superior Province. The lamprophyres have ε _Nd ²⁷⁰⁰ values of +1.4 to +2.0, indicating derivation from a depleted mantle source. Growth curves on an ε _Nd vs. age diagram are consistent with the extraction of the lamprophyres from a depleted source (Sm/Nd>chondrite) just prior to 2700 Ma, the accepted age of the VGC. The lamprophyres have fractionated REE patterns (Ce/Yb_n=10–15) that indicate genesis by a) 1% to 3% fusion of a pristine garnet lherzolite or b) ～10% fusion of an enriched mantle source. However, consideration of the pressure of melting and elemental plots of Al and Ti indicate that garnet was not a residual phase during lamprophyre genesis. Thus, the enrichment of the LREE (80–100 x chondrite), Sr (580–1400 ppm), and Ba (590–1600 ppm) indicate derivation from an enriched mantle. These apparently contradictory chemical characteristics can be reconciled if the source region of the lamprophyres was depleted over a period of time but subsequently enriched just prior to genesis of the lamprophyre magmas. It is suggested that the source of the enriched component may have been fluids derived from dehydration of a subducting ocean crust.  相似文献   

ANNUAL BUSINESS MEETING ANN ARBOR,AUGUST 13, 1969     

Wesley C. Calef 《The Professional geographer》1969,21(6):413-415

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Foreword     

Dr. Wesley T. Huntress Jr. Dr. 《Earth, Moon, and Planets》1994,67(1-3):vii-vii

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Origin of the structure and planform of small impact craters in fractured targets: Endurance Crater at Meridiani Planum, Mars     

Wesley A. Watters  John P. Grotzinger  John Grant  Rongxing Li  Maria T. Zuber 《Icarus》2011,211(1):472-497

We present observations and models that together explain many hallmarks of the structure and growth of small impact craters forming in targets with aligned fractures. Endurance Crater at Meridiani Planum on Mars (diameter ≈ 150 m) formed in horizontally-layered aeolian sandstones with a prominent set of wide, orthogonal joints. A structural model of Endurance Crater is assembled and used to estimate the transient crater planform. The model is based on observations from the Mars Exploration Rover Opportunity: (a) bedding plane orientations and layer thicknesses measured from stereo image pairs; (b) a digital elevation model of the whole crater at 0.3 m resolution; and (c) color image panoramas of the upper crater walls. This model implies that the crater’s current shape was mostly determined by highly asymmetric excavation rather than long-term wind-mediated erosion. We show that modal azimuths of conjugate fractures in the surrounding rocks are aligned with the square component of the present-day crater planform, suggesting excavation was carried farther in the direction of fracture alignments. This was previously observed at Barringer Crater in Arizona and we show the same relationship also holds for Tswaing Crater in South Africa. We present models of crater growth in which excavation creates a “stellate” transient cavity that is concave-cuspate in planform. These models reproduce the “lenticular-crescentic” layering pattern in the walls of some polygonal impact craters such as Endurance and Barringer Craters, and suggest a common origin for tear faults and some crater rays. We also demonstrate a method for detailed error analysis of stereogrammetric measurements of bedding plane orientations.  相似文献   

IUGS Commission on Geoscience Edoucation, Training and Technology Transfer （COGE） http ：//www.geoed.com.au/IUGSeducation/indexcomm.html     

Gary Lewis Wesley Hill 《《幕》》2006,29(4):310-311

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